The following invention relates to a solution and a method of using that solution for treating printed circuit boards to prevent smear in the manufacture thereof.
During the manufacture of printed circuit ducting copper layers sandwiching a glass epoxy layer, holes are drilled which are then electroplated to create a circuit path from one copper layer to the other In multilayer boards there can be intermediate copper layers as well. When these holes are drilled, a phenomenon known as "smear" may result Smear is a dielectric material which is deposited on the inner surfaces of the holes made by the drill. The smeared inner walls of the drilled-out holes resist electroplating or the electroless deposit of copper and the smeared material may also effectively cover inner copper conductive layers in multi-layer boards creating a void such that no electrical contact is made between the inner walls of the hole and the inner conductive layers.
Smear is an industry-wide problem in the manufacture of printed circuit boards, and many approaches have been suggested as solutions The most common approach, called "etchback", is to attempt to remove the smear after the holes have been drilled Smear removal generally takes the form of immersing the boards in a strong sulfuric acid bath to roughen or remove the smear and then subsequently rinsing the boards. This approach is expensive and leads to other problems such as residues left by the sulfuric acid which also interfere with the electroplating of the printed circuit board holes. Other approaches use chemicals other than sulfuric acid; nevertheless in these processes, it is necessary to treat the board after the holes have been drilled and then to rinse the treatment chemical away. The rinsing step, in particular, may be extremely time consuming and the equipment needed for post drilling treatment of the boards for any type of smear removal process is very expensive.